.\" -*- nroff -*-
.\" Copyright 2010 Cisco Systems, Inc.  All rights reserved.
.\" Copyright 2006-2008 Sun Microsystems, Inc.
.\" Copyright (c) 1996 Thinking Machines Corporation
.\" $COPYRIGHT$
.TH MPI_Start 3 "Jun 10, 2020" "4.0.4" "Open MPI"
.SH NAME
\fBMPI_Start\fP \- Initiates a communication using a persistent request handle.

.SH SYNTAX
.ft R
.SH C Syntax
.nf
#include <mpi.h>
int MPI_Start(MPI_Request *\fIrequest\fP)

.fi
.SH INPUT PARAMETER
.ft R
.TP 1i
request
Communication request (handle).

.SH OUTPUT PARAMETER
.ft R
.TP 1i
IERROR
Fortran only: Error status (integer).

.SH DESCRIPTION
.ft R
A communication (send or receive) that uses a persistent request is initiated by the function MPI_Start.
.sp
The argument, request, is a handle returned by one of the persistent communication-request initialization functions (MPI_Send_init, MPI_Bsend_init,  MPI_Ssend_init, MPI_Rsend_init, MPI_Recv_init). The associated request should be inactive and becomes active once the call is made.
.sp
If the request is for a send with ready mode, then a matching receive should be posted before the call is made. From the time the call is made until after the operation completes, the communication buffer should not be accessed.
.sp
The call is local, with semantics similar to the nonblocking communication operations (see Section 3.7 in the MPI-1 Standard, "Nonblocking Communication.") That is, a call to MPI_Start with a request created by MPI_Send_init starts a communication in the same manner as a call to MPI_Isend; a call to MPI_Start with a request created by MPI_Bsend_init starts a communication in the same manner as a call to MPI_Ibsend; and so on.

.SH ERRORS
Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object.
.sp
Before the error value is returned, the current MPI error handler is
called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error.

.SH SEE ALSO
.ft R
.sp
MPI_Bsend_init
.br
MPI_Rsend_init
.br
MPI_Send_init
.br
MPI_Sssend_init
.br
MPI_Recv_init
.br
MPI_Startall


